1. Field of the Invention
The present invention relates to thermoplastic resin compositions and injection molded articles produced therefrom. In particular, the invention relates to a thermoplastic resin composition which is superior in moldability due to its superior fluidity and from which molded articles superior in rigidity, impact resistance and appearance can be produced by injection molding. It should be noted that in the present invention, the appearance of molded articles corresponds mainly to the condition of flow marks in the molded articles.
2. Description of the Related Art
Polypropylene-based resin has been used widely in materials required to have rigidity, impact strength and the like. Polypropylene-based resin has recently been used widely, particularly, as materials for automobiles, and especially, ethylene-propylene block copolymers are used increasingly. Although ethylene-propylene block copolymers have conventionally been produced by the solvent method, the ethylene-propylene block copolymers have recently been produced by the continuous gas phase method which comprises a simple production process and by which the ethylene-propylene block copolymer can be produced at low cost.
However, an ethylene-propylene block copolymer produced by the gas phase method has a low swelling ratio due to the lower intrinsic viscosity of its ethylene-propylene copolymer portion and, therefore, molded articles produced therefrom have poor appearance due to the occurrence of unfavorable flow marks. When the intrinsic viscosity of the ethylene-propylene copolymer portion of the ethylene-propylene block copolymer produced by the gas phase method is increased, hard spots are formed and molded articles produced therefrom have poor appearance.
For solving the problems regarding appearance described above, JP-A-07-286022, for example, discloses a propylene-based block copolymer produced by a batchwise solvent method, a n-decane(23° C.)-insoluble component of which has an intrinsic viscosity of 0.1 to 20 dl/g, a n-decane(23° C.)-soluble component of which has an intrinsic viscosity of 5 to 15 dl/g, and from which molded articles can be formed without the formation of hard spots. However, as disclosed in Comparative Example 3 in the above-cited document, when the n-decane(23° C.)-soluble component, which probably is an ethylene-propylene block copolymer portion, contained in an ethylene-propylene block copolymer has a high intrinsic viscosity, the ethylene-propylene block copolymer contains many rubber particles which will cause hard spots.
JP-A-07-286075 discloses a propylene polymer composition which comprises a propylene polymer produced by a continuous method and an ethylene-propylene block copolymer containing a n-decane(23° C.)-soluble component having an intrinsic viscosity of 5 to 12 dl/g and from which composition molded articles can be formed without the formation of hard spots. However, the amount of the ethylene-propylene block copolymer compounded is as large as 12% by weight or more.